研究基因剔除平衡型核苷轉運蛋白2對亨丁頓舞蹈症模式的小鼠疾病進程的影響

Abstract

亨丁頓舞蹈症是一種顯性體染色體遺傳疾病，源於位於第四對染色體上的亨丁頓基因具有過長的CAG重複序列，因而產生變異的且有毒的亨丁頓蛋白。目前對於亨丁頓舞蹈症並無有效的延緩疾病或是治癒的方法，只能給予支持性的治療。腺苷在腦中的基礎調控機制中扮演很重要的角色。近期有許多研究發現在亨丁頓舞蹈症的病人腦中及疾病小鼠的腦中，腺苷的恆定有被異常調控的現象。而在腦中主要維持腺苷恆定的兩種轉運蛋白為平衡型核苷轉運蛋白1及2 (Ent1及Ent2)，其中又以Ent2在腦中的表現量較多。本研究的目的在探討基因剔除Ent2對於亨丁頓症小鼠(R6/2)疾病進展之影響。剔除Ent2的R6/2小鼠(R6/2-Ent2-/-)以及其同窩對照組( R6/2-Ent2+/+)經由R6/2-Ent2+/-小鼠及CBA-Ent2+/-小鼠配對而得。而R6/2-Ent2+/-以及CBA-Ent2+/-小鼠則分別經由配對CBA-Ent2-/- 與R6/2 小鼠以及配對Ent2-/- (C57BL/6-Slc29a2em1) 與CBA (CBA/CaJNarl)小鼠而得。小鼠之運動功能以滾輪運動測試、四肢緊縮測驗以及步態分析等行為測試評估。除此之外，也記錄其生命週期。結果顯示將平衡型核苷轉運蛋白2剔除後，R6/2小鼠無論在滾輪運動測試、四肢緊縮測驗及生命週期等方面皆具有惡化現象。雖然確切影響機致仍有待釐清，本研究的結果顯示平衡型核苷轉運蛋白2在亨丁頓氏症的疾病進展上扮演重要角色。

Huntington’s disease (HD) is an inherited autosomal dominant disorder caused by mutant huntingtin protein translated from HTT gene with an expansion of CAG repeats in the exon1.To date, the treatment of HD is still an unmet medical need. Adenosine plays an important role in modulating several functions in the brain, while recent studies have shown that adenosine homeostasis is aberrantly regulated in the brain of animal models and patients of HD. Equilibrative nucleoside transporter 1 (Ent1) and Ent2 are the major transporters responsible for brain uptake of adenosine, in which the expression of Ent2 is generally higher than that of Ent1. The objective of the present study was to investigate the impacts of Ent2 knockout on disease progression of a mouse model of HD (R6/2 mice). R6/2-Ent2-/- mice and the littermate controls (i.e., R6/2-Ent2+/+) were obtained by crossing R6/2-Ent2+/- mice with CBA-Ent2+/-. R6/2-Ent2+/- and CBA-Ent2+/- mice were obtained by crossing CBA-Ent2-/- mice and R6/2 mice and by crossing Ent2-/- (C57BL/6-Slc29a2em1) and CBA (CBA/CaJNarl), respectively. Motor function was evaluated by rotarod performance, limb-clasping score, and gait analysis. Also, lifespan was recorded. The results showed the Ent2 deletion caused detrimental effects on the rotarod performance, limb-clasping, and gait function. It also tended to decrease lifespan of R6/2 mice. Although the mechanisms underlying these effects are to be verified, these results suggest that Ent2 plays an important role in disease progression of R6/2 mice.